Question: Tiffany is 27 years younger than Kevin. Seven years ago, Kevin was 4 times older than Tiffany. How old is Kevin now?
Answer: We can use the given information to write down two equations that describe the ages of Kevin and Tiffany. Let Kevin's current age be $k$ and Tiffany's current age be $t$ The information in the first sentence can be expressed in the following equation: $k = t + 27$ Seven years ago, Kevin was $k - 7$ years old, and Tiffany was $t - 7$ years old. The information in the second sentence can be expressed in the following equation: $k - 7 = 4(t - 7)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $k$ , it might be easiest to solve our first equation for $t$ and substitute it into our second equation. Solving our first equation for $t$ , we get: $t = k - 27$ . Substituting this into our second equation, we get the equation: $k - 7 = 4($ $(k - 27)$ $ -$ $ 7)$ which combines the information about $k$ from both of our original equations. Simplifying the right side of this equation, we get: $k - 7 = 4k - 136$ Solving for $k$ , we get: $3 k = 129$ $k = 43$.